It took Antoine Leiris under an hour to compose his powerful Facebook reaction to the murder of his wife, Hélène Muyal-Leiris, who died at the Bataclan theater in Paris. Terrorists slaughtered 89 people there during a concert by the band Eagles of Death Metal on Nov. 13, 2015.

“The words came into my head for 45 minutes and the actual writing took less than 15 minutes,” the Frenchman tells The Post. “I wanted our friends and family to know that this was the way my son and I chose to act; the way we wanted to go.”

‘She will be with us, invisible, but there. It is in our eyes that you will read her presence, in our joy that her flame will burn, in our veins that her tears will flow’

As he addressed Hélène’s killers via social media on the same day he viewed her body in a mortuary, he had no idea of the effect his words would have on the world. The message was shared 230,000 times on Facebook and picked up by newspapers and TV stations across the globe.

“On Friday night, you stole the life of an exceptional human being, the love of my life, the mother of my son, but you will not have my hate,” Antoine wrote, adding that he would not give the terrorists the “satisfaction” of fear. He finished by describing how his and Hélène’s toddler, Melvil, would defy the attackers “by being happy and free.”

Nearly a year later, the 35-year-old journalist has written “You Will Not Have My Hate.” Out Tuesday, it’s a heartbreaking account of his two weeks after Hélène’s killing.

The book recalls how he was at home watching Melvil on the night of Nov. 13 when he received a text message from a friend asking if everything was OK. Rock music fan Hélène, 35, was attending the concert with a friend. Antoine turned on the TV and saw the reports of the terrorist attacks.

“I feel an electric shock go through my body. I want to run outside, steal a car, go out and look for her. But I’m paralyzed because Melvil, 17 months old, is with me,” he writes. “I want to scream, but it’s impossible. Do not wake the baby.”

He recounts how, once relatives arrived to baby-sit, he and his brother frantically drove to the hospitals where the injured were taken.

They finally abandoned the search at 7 a.m.

Police officers stand guard in front of the main entrance of Bataclan concert hall following the terror attacks on November 16,

“I said: ‘We have to go because I have to give a bottle to my son in half an hour,’ ” Antoine tells The Post. “I was thinking: ‘If I have to be a full-time father, then it has to start the first day.’ ”

It turned out that rigidly following Melvil’s daily routine — dressing, diapering, eating — helped him stay in the moment and not give into his fears.

“I invested myself 100 percent in fatherhood. It’s a way for me to survive and continue living.”

It was in this spirit that he accepted the devastating news that Hélène, his partner of 12 years, was dead, writing in his book of how his life — and Melvil’s — would somehow go on without her.

‘If you look hatred in the eyes, you will see what she brings with her — a lifetime of hate’

“With a burst of machine gun fire, [the terrorists] shattered our puzzle,” writes Antoine. “And after we have put it back together, piece by piece, it will no longer be the same. There will be . . . only the two of us, but we will take up the whole picture.

“She will be with us, invisible, but there. It is in our eyes that you will read her presence, in our joy that her flame will burn, in our veins that her tears will flow.”

Asked how he feels about the people who criticized his standpoint of not hating, Antoine is circumspect. He understands their point of view, but suggests they see things from a different perspective.

“Many times I wanted to hate [the killers] and just escape from Paris and the world,” Antoine says. “You can give into that instinct or reflect on it.

“If you look hatred in the eyes, you will see what she brings with her — a lifetime of hate.”

As for the future, Antoine — who is fiercely protective of his family’s privacy and withholds certain details in his book and interviews to respect his intimacy with Hélène — is awaiting Nov. 14, 2016, when he will “disappear from public life.”

“It will be a year since the attacks,” he says. “Like many of the people who lived them, I see the important date of Nov. 13. After that, it will be the start of something new.”